A secondary battery can be repeatedly charged and discharged, which is widely used in small-sized portable electronic devices such as cellphones, notebooks and the like, and is also widely used in vehicles such as hybrid electric vehicles, pure electric vehicles and the like. In a process of fast charging or high-power discharging, the interior of the secondary battery will generate excessive heat, and electrolyte may be decomposed. Generation of the heat and decomposition of the electrolyte increase the internal pressure of the secondary battery, which may lead to fire and explosion of the secondary battery, and thus reduce safety of the secondary battery.
In the related art, the secondary battery is usually provided with a contact plate, the contact plate is attached to a negative terminal, and a top cover plate is electrically connected with a positive terminal. When the internal pressure of the secondary battery exceeds a reference pressure, the contact plate deforms under gas pressure and is in electrical contact with the top cover plate, resulting in an external short-circuit between a positive electrode plate and a negative electrode plate.
In above solutions, the contact plate is attached to the negative terminal, in order to prevent corrosion of the contact plate, a standard electrode potential of the contact plate should be greater than 0.000V (e.g., copper material selected). However, the top cover plate is positively-charged due to its electrical connection with the positive terminal, corrosion is not serious, as a result, materials with more excellent processability and lower cost can be selected (e.g. aluminum, steel). Since the contact plate and the top cover plate adopt different materials, a resistivity of the top cover plate is greater than a resistivity of the contact plate, and the difference therebetween is relatively large, when the contact plate is in electrical contact with the top cover plate, a contact resistance therebetween is very high, so that an area on the top cover plate where the top cover plate is in contact with the contact plate will generate a large amount of heat. In this case, the top cover plate or the contact plate may easily get fused due to rapid increasing of temperature, which cannot maintain the external short-circuit state between the positive electrode plate and the negative electrode plate, and thus reduce safety of the secondary battery.